Reduced Graphene Oxide Reinforces Boron Carbide with High-Pressure and High-Temperature Sintering

Introducing a second phase has been an effective way to solve the brittleness of boron carbide (B4C) for its application. Though reduced graphene oxide (rGO) is an ideal candidate for reinforcing the B4C duo’s two-dimensional structure and excellent mechanical properties, the toughness is less than 6 MPa·m1/2, or the hardness is lower than 30 GPa in B4C–graphene composites. A barrier to enhancing toughness is the weak interface strength between rGO and B4C, which limits the bridging and pull-out toughening effects of rGO. In this work, internal stress was introduced using a high-pressure and high-temperature (HPHT) method with B4C–rGO composites. The optimal hardness and toughness values for the B4C-2vol%rGO composite reached 30.1 GPa and 8.6 MPa·m1/2, respectively. The improvement in toughness was 4 times higher than that of pure B4C. The internal stress in the composite increased gradually from 2.3 GPa to 3.3 GPa with an increase in rGO content from 1vol%to 3vol%. Crack deflection, bridging, and rGO pull-out are responsible for the improvement in toughness. Moreover, the high internal stress contributed to the formation of good interface strength by embedding rGO into the B4C matrix particles, which further enhanced the dissipation of the crack energy during the pull-out process and led to high toughness. This work provides new insights into synthesizing high-toughness B4C matrix composites.